CI: allow the wheel build commit trigger anywhere in the commit message
CI: allow the wheel build commit trigger anywhere in the commit message

This trigger is: [wheel build]

Before it had to be on the first line, which is out of sync with
other such commands like `[skip azp]` and `[skip circle]`.

So this commit message in a PR now should trigger a wheel build.

rgommers/scipy,andyfaff/scipy,scipy/scipy,Stefan-Endres/scipy,WarrenWeckesser/scipy,ilayn/scipy,mdhaber/scipy,endolith/scipy,WarrenWeckesser/scipy,ilayn/scipy,ilayn/scipy,andyfaff/scipy,mdhaber/scipy,endolith/scipy,ilayn/scipy,ilayn/scipy,mdhaber/scipy,endolith/scipy,mdhaber/scipy,scipy/scipy,scipy/scipy,scipy/scipy,andyfaff/scipy,WarrenWeckesser/scipy,endolith/scipy,andyfaff/scipy,anntzer/scipy,andyfaff/scipy,Stefan-Endres/scipy,scipy/scipy,Stefan-Endres/scipy,mdhaber/scipy,Stefan-Endres/scipy,anntzer/scipy,Stefan-Endres/scipy,endolith/scipy,mdhaber/scipy,anntzer/scipy,rgommers/scipy,rgommers/scipy,Stefan-Endres/scipy,anntzer/scipy,rgommers/scipy,anntzer/scipy,scipy/scipy,WarrenWeckesser/scipy,endolith/scipy,andyfaff/scipy,WarrenWeckesser/scipy,WarrenWeckesser/scipy,rgommers/scipy,anntzer/scipy,ilayn/scipy